10/8/2010
Meeting 11
Cryptography
What is cryptography
The term cryptography is derived from Greek,
kryptos means “hidden” or “secret” and graphy
means “writing”. So, cryptography is the practice
and study of creating a secret information.
Cryptography works by Cryptography is a part of
mathematics and computer science.
Cryptography is used in applications present
in technologically advanced societies; examples
include the security of ATM cards, computer
passwords, and electronic commerce, which all
depend on cryptography. In short we can say that
cryptography is needed to secure a secret
document. A person who is master in
cryptography is called cryptographer.
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How cryptography works
For example someone has a secret
document to secure. Any document can be
secured using cryptography. For example we
have to secure the word “Read” using
cryptography. The word “Read” in cryptography
is called Plain text. Using a set of rule called
algorithm, the plain text is changed into cipher
text. This process is called encryption. The result
of this encryption process is the word “Uhdg”.
This is the cipher text.
A set of rule (algorithm) that is used in
encryption can be different. There are
many algorithm used in encryption. At the
above example we use Caesar Cipher
algorithm that is used by Julius Caesar to
secure his document.
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The reverse process of encryption is called
decryption. The input is a cipher text. And the
result of decryption process is plain text.
Task 2
Show whether the followings statements
are true or false (T/F) from Slide 2 - 5.
1. Cryptography is the practice and study of
creating a secret information.
2. Not all document can be secured using
cryptography.
3. Using a set of rule called algebra, the plain
text is changed into cipher text.
4. The word “kryptos” is a Latin origin.
5. The reverse process of encryption is called
decryption.
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History of cryptography
Cryptography is already used since ancient
era. Julius Caesar used cryptography to secure
his message from his enemy. He replaced a
character with its next three character. For
example a character ‘A’ in alphabet will be
replaced by character ‘D’. And so on. See the list
below of Julius Caesar algorithm.
• Plain text :abcdefghIjklmnopqr
stuvwxyz
• Cipher Text :defghIjklmnopqrstu
vwxyzabc
In the era of World War II,
German Nazi was also used
cryptography to secure its
message. Nazi used a machine
called Enigma to encrypt and
decrypt the messages. In this
way Nazi thought its message
would be difficult to break by US
and its allies. Below is a picture
of Enigma used by Nazi.
Unfortunately the algorithm of Enigma can
be broken by US army.
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In computer technology, cryptography
is still used to secure a computer data or
document. For example in ATM machine,
computer passwords, and also in
electronic commerce. Using computer
technology someone can use many
sophisticated algorithm for example RSA,
DES, and PGP.
COMPUTER TERMS
• Plain text = a text that can be read by anybody.
This text is not secured yet.
• Cipher text = a secret text resulting from
encryption process.
• Algorithm = a set of rule to encrypt a document.
• Enigma = a machine like typewriter that is used
by Nazi during World War II to secure
a document before transmitted.
• Cryptographer = a person who is master in
cryptography.
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Task 2
Figure out this message.
“BRX KDYH MXVW GLVFRYHUHD WKH
DQFLHQW VHFUHW FRGLQJ FDOOHG
MXOLXV FDHVDU DOJRULWKP”
What does it say?
___________________________________
___________________________________
mhtirogla raseaC suiluJ esU
FURTHER READINGS
• http://en.wikipedia.org/wiki/Cryptography
• http://en.wikipedia.org/wiki/Cryptography_Classification
• http://en.wikipedia.org/wiki/Encyclopedia_of_Cryptography_and_Security
• http://en.wikipedia.org/wiki/Japanese_cryptology_from_the_1500s_to_Meiji
• http://en.wikipedia.org/wiki/List_of_important_publications_in_computer_science#Cry
ptography
• http://www.merriam-webster.com/dictionary/cryptology/
• http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf
• http://www.cesg.gov.uk/site/publications/media/notense.pdf
• http://citeseer.ist.psu.edu/cache/papers/cs/22094/http:zSzzSzeprint.iacr.orgzSz2001z
Sz056.pdf/junod01complexity.pdf
• http://www.rsasecurity.com/rsalabs/node.asp?id=2152
• http://www.ieee-security.org/Cipher/Newsbriefs/1996/960214.zimmerman.html
• http://www.schneier.com/crypto-gram-0006.html#DES
• http://scholar.google.com/url?sa=U&q=http://www.springerlink.com/index/K54H077N
P8714058.pdf
• http://www.cacr.math.uwaterloo.ca/hac/
• http://www.cryptool.org/download/CrypToolPresentation-en-1_4_20.pdf
• http://www.rsasecurity.com/rsalabs/node.asp?id=2152
• http://www.pawlan.com/Monica/crypto/
• http://www.nsa.gov/kids/
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